A system for checking the pressure of the tires of a motor vehicle includes, around a central computer equipped with a receiver, with its receiving antenna, individual checking devices, one per wheel, each comprising, inserted into the rim, a pressure sensor and a transmitter, with its transmitting antenna. Each device has to transmit regularly, to the central computer, bursts of information bits relating to the pressure of the associated tire, and it has to transmit a defined number of them, generally five, all identical, so that another defined number, generally two, of these bursts should be received and so that it can therefore be considered that the information at that instant has actually been transmitted and received. The transmission of the bursts can take place, to give an idea, every hour, if the vehicle is at rest, every six minutes, if the vehicle is running.
The system developed above exhibits the drawback that, after having changed the wheels, the system may detect a lack of pressure at one wheel which is not actually a faulty wheel. With the bursts of information bits being in effect xe2x80x9csignedxe2x80x9d by their respective wheels, if, for example, the two front wheels are changed over and then the pressure of the left wheel falls, the system will indicate that it is the original right wheel, which has become the left wheel, which is faulty.
DE 195 18 806 teaches a radio system for checking the pressure of the tires, with antennae associated electromagnetically with the locations of the respective wheels, in order to identify them.
However, as the transmitter devices of the wheels are mutually independent, their transmissions are asynchronous and the central receiver has to be able to detect every start-of-transmission so as to synchronize itself and to receive the information transmitted.
The present application claims to have a solution to this problem.
The invention thus relates to a system for checking the pressure of the tires of the wheels of a vehicle including individual wheel-checking devices, each with a pressure sensor and a transmitter, a central unit with a common receiver and antenna means, comprising individual receiving antennae associated respectively with the wheel locations, configured to work with the transmitters of the individual checking devices, the system being characterized in that the receiving-antenna means of the central unit additionally comprise a main antenna for monitoring all the pressure-checking devices and means for switching over the common receiver of the central unit from the main monitoring antenna onto each of the individual acquisition antennae.
Thus, with the main monitoring antenna having made it possible to detect the failure of a tire, as yet undefined, one of the individual antennae will make it possible to acquire the identification of the tire concerned. Any difficulty relating to the asynchronous transmission from the wheel devices is thus avoided.
Advantageously, with the wheel-checking devices being configured to periodically transmit bursts of information bits, the changeover-switching means are configured to switch over from the main receiving antenna onto an individual receiving antenna in the course of the same burst period.
If, after switching over, the common receiver receives the rest of the bursts, then it is the wheel tire associated with the individual antenna concerned which is actually the faulty tire. Otherwise, the following burst period will be awaited in order to switch over to another individual antenna and so on until the faulty wheel tire has been identified.
Very advantageously, the receiving antennae are radiating cables.